1. Field of the Invention
The present invention relates to a heat-dissipating device of a semiconductor device and to a method of manufacturing the semiconductor device, and more particularly to a heat-dissipating device of a semiconductor device, and method of fabricating the semiconductor device, in which the wiring substrate on which semiconductor chips are mounted is realized as a plurality of substrates, and further, which has a plurality of heat-dissipating structures.
2. Description of the Related Art
In conjunction with the advance in the number and variety of functions of semiconductor chips, which are assemblages of semiconductor elements (for example, LSI and IC), advances have been made in LSI packaging in which a plurality of substrates that secure semiconductor chips are electrically and mechanically joined to a wiring substrate. One issue that must be solved in such configurations, in which a wiring substrate and a group of LSI make up a single structure, is the occurrence of thermal stress that accompanies securing by mechanical joining.
The technique for solving this problem that is disclosed in Japanese Patent Laid-open No. 150735/2000 has received considerable attention. This known technique suppresses the occurrence of thermal stress by incorporating a heat-dissipating structure in a mechanically mounted structure that includes a first mounting body, in which semiconductor chips are mounted on a substrate, and a second mounting body in which the first mounting body is mounted on a wiring substrate. Although this known technique realizes the unified incorporation of a heat-dissipating structure in a two-layered mechanical structure, it apparently gives no information regarding the transmission characteristic of output signals that are outputted by chips.
A method is sought to suppress deterioration of the transmission characteristic of a multiple-structure package in which two types of substrates are joined and secured and which is provided with a heat-dissipating structure. A method is also sought to facilitate the assembly of this type of multiple-structure package.
It is an object of the present invention to provide a heat-dissipating device of a semiconductor device that can suppress deterioration of the transmission characteristic of a multiple-structure package in which two types of substrates are joined and secured and which is provided with a heat-dissipating structure. It is also an object of the present invention to provide a method of fabricating such a device.
A means of achieving this object is described hereinbelow. The technical items that appear in this description are assigned numbers or symbols in parentheses. These numbers or symbols coincide with the reference numbers or reference symbols that are assigned to the technical items that constitute at least one embodiment or a plurality of the working examples from among the plurality of embodiments or plurality of working examples of the present invention, and in particular, to the technical items that appear in the drawings that correspond to these embodiments or working examples. These reference numbers and reference symbols clarify the correspondence between and the technical items described in the claims and the technical items of the embodiments or working examples. However, this correspondence does not imply that the technical items described in the claims should be interpreted as being limited to the technical items of the embodiments or working examples.
A heat-dissipating device of a semiconductor device according to the present invention is constituted from:
a first wiring substrate (1) on which semiconductor elements (7) are mounted;
a second wiring substrate (2) that supports the back surface of the first wiring substrate 1, i.e., the surface of the first wiring substrate (1) that is on the opposite side from a first substrate active surface (4), which is the surface on which the semiconductor elements (7) are mounted;
a heat dissipator (9) that is thermally and mechanically joined to the back surfaces of the semiconductor elements 7, which are the surfaces of the semiconductor elements (7) that are on the opposite sides from the semiconductor element surfaces that confront the first substrate active surface (4); and
conductors (6) that extend, in the planar direction of the first substrate active surface (4) or a plane that approaches that of the first substrate active surface (4), from said first substrate active surface (4) as far as an electrical junction surface (5) of the second wiring substrate [2].
The conductors (6) extend in a straight line (linearly) that does not bend in the direction of the layers (an orthogonal direction that is orthogonal to the first substrate active surface 4).
This definition means that the plane that contains the first substrate active surface (4) of the first wiring substrate (1) and the plane that contains the electrical junction surface (5) of the second wiring substrate 2 form the same plane, or that the plane that contains the first substrate active surface (4) of the first wiring substrate (1) and the plane that includes the electrical junction surface (5) of the second wiring substrate 2 are parallel and, moreover, are separated by a distance that approaches zero and is substantially zero. The length of the conductors (6) is therefore minimized, and the harmonic transmission characteristic is excellent.
In a heat-dissipating structure in which a heat dissipator (9), semiconductor elements (7), and the first wiring substrate (1) are stacked in this way, the conductors 6, which are geometrically limited because the electrical junction point area of the second wiring substrate 2 cannot overlap with the heat-dissipating structure, extend in a planar direction due to the three-dimensional arrangement in which the distance of separation in an orthogonal direction, which is orthogonal to the planar direction, between the first substrate active surface (4) and the electrical junction surface (5) is substantially close to zero, whereby the length of the conductors is minimized. A distance of separation that is substantially close to zero can be achieved because the distance is less than the thickness of the first wiring substrate 1.
The length of the conductors 6 does not include the distance between the edge of the first wiring substrate (1) and the edge of the second wiring substrate (2). As will be shown in FIG. 2 described hereinbelow, this reduced length can be achieved because the two edges are in contact. The first wiring substrate (1) is set into the second wiring substrate 2 in the previously described orthogonal direction. This insetting allows the distance of separation between the first substrate active surface (4) and the electrical junction surface (5) to approach zero.
The heat dissipator (9) is preferably joined to the semiconductor elements with a heat conductive adhesive layer 8 interposed. A stacked heat dissipator (12), which is thermally and mechanically joined with an interposed heat conductive buffer layer (11) to the heat-dissipating surface of the heat dissipator (9) on the side of the heat dissipator (9) that is opposite the side on which the semiconductor elements (7) are arranged; and supports (21), which support the stacked heat dissipator (12) on the first wiring substrate (1), are also added. This stacked heat dissipator (12) has a more extensive heat-dissipating surface than the heat dissipator (9).
The stacked heat dissipator (12) is supported by the first wiring substrate (1) but is not supported by the first wiring substrate (1) via the heat dissipator (9) and the semiconductor elements (7), and the semiconductor elements (7) therefore do not receive the stress imposed by a massive stacked heat dissipator (12). The supports (21) may be formed by a portion of the heat dissipator (9). Another heat conductive adhesive layer (22) is preferably provided between the supports (21) and the first wiring substrate (1).
Spacers (14) are interposed between the stacked heat dissipator (12) and the second wiring substrate (2). In addition to functioning as supports for supporting the stacked heat dissipator (12) on the second wiring substrate 2, these spacers (14) have the important function of fixing the distance of separation between the stacked heat dissipator (12) and the first wiring substrate (1) and preventing the thermal stress of the stacked heat dissipator 12 from being conveyed by direct propagation by way of the heat dissipator (9) to the semiconductor elements (7). To further ensure this function, it is important that a heat conductive buffer layer (11) be interposed between the stacked heat dissipator (12) and the supports (21). Still stronger joining between stacked heat dissipator (12) and second wiring substrate (2) can be obtained by means of bolts 15 that pass through these spacers due to the regulation of the distance of separation.
The area of the second wiring substrate (2) is greater than that of the first wiring substrate (1). The second wiring substrate (2) has a depression (3) in the orthogonal direction, which is orthogonal to the surface of the first substrate active surface (4); and the first wiring substrate (1) is set into this depression (3). Forming this depression (3) causes the previously described distance of separation to substantially approach zero. The depression 3 can be formed as an opening that penetrates in the previously described orthogonal direction.
An additional heat dissipator (17) is joined to the second wiring substrate 2. This additional heat dissipator (17) is thermally and mechanically joined to the periphery around the opening (3) in second wiring substrate (2). An additional heat conductive buffer layer (16) is preferably interposed between the first wiring substrate (1) and this additional heat dissipator (17). The heat conductive buffer layer (16) is arranged inside the opening (3). This heat conductive buffer layer (16) effectively absorbs the thermal stress of the additional heat dissipator (17) and suppresses the transmission of this thermal stress to the first wiring substrate (1).
The heat dissipator (9) is provided with: a plurality of joining portions for joining to the plurality of semiconductor elements (7); and a single main body portion that is both thermally and mechanically joined as a unit to this plurality of joining portions. Heat that is generated from the plurality of semiconductor elements (7) flows to the main body portion and is effectively dissipated by way of the heat-dissipating surface of the main body portion, and moreover, can be even more effectively dissipated by the extensive heat-dissipating surface (13) of the stacked heat dissipator (12) that is joined to the main body portion. A heat conductive buffer layer (11) is interposed in the heat conduction path of this heat dissipation and simultaneously absorbs heat and thermal stress. The semiconductor elements (7) are preferably joined to the joining portions with a first heat conductive adhesive layer (8) interposed.
It is particularly preferable that a second heat conductive adhesive layer (22) be interposed between the supports (21) and the first wiring substrate (1), and moreover, that spacers (14) be interposed between the stacked heat dissipator (12) and the second wiring substrate (2). As previously described, a more solid connection is preferably obtained between the stacked heat dissipator (12) and the second wiring substrate (2) by means of bolts that pass through the spacers (14).
The heat-dissipating device of a semiconductor device according to the present invention is thus constituted by a first heat-dissipating structure and a second heat-dissipating structure. The first heat-dissipating structure is provided with: the first wiring substrate (1), a plurality of semiconductor elements (7) that are mounted on the first wiring substrate (1), and a first heat dissipator (9) that is thermally and mechanically joined to the plurality of semiconductor elements (7). The second heat-dissipating structure is provided with: a second wiring substrate (2) and a second stacked heat dissipator (12) that is supported on the second wiring substrate (2). The first wiring substrate (1) is electrically connected to the second wiring substrate (2) by means of conductors (6) each having one end electrically joined to the first wiring substrate (1) and the other end electrically joined to the second wiring substrate (2).
The first substrate active surface (4) of the first wiring substrate (1), to which one end of each conductor is joined, is substantially parallel to the second substrate surface (5) of the second wiring substrate (2), to which the other end of each conductor is joined, and the effective distance between the plane that contains the first substrate active surface (4) and the plane that contains the second substrate surface (5) is substantially close to zero. The configuration of the arrangement of the plurality of wiring substrates that are incorporated within the multilayered heat-dissipating structure is flat, whereby a minimum length of conductors (6) can be realized within this flat structure. This flat structure can be defined by stipulating that the second wiring substrate (2) is not present between the first substrate surface (4) of the first wiring substrate (1) and the first heat dissipator (9). The effective distance can be defined as shorter than the thickness of the first wiring substrate 1.
The fabrication method of a semiconductor device according to the present invention is constituted by steps of:
mounting a plurality of semiconductor elements (7) on a first wiring substrate (1);
first joining for thermally and mechanically joining a first heat dissipator (9) to the plurality of semiconductor elements (7);
second joining for mechanically joining the first heat dissipator (9) to the first wiring substrate (1);
third joining for electrically joining the first wiring substrate (1) and the second wiring substrate (2) by conductors (6) that extend in a planar direction that is substantially parallel to the first substrate active surface (4) of the first wiring substrate (1) and the second substrate surface (5) of the second wiring substrate (2);
fourth joining for mechanically joining a second heat dissipator (12) to the second wiring substrate (2) with spacers (14) interposed; and
fifth joining for thermally and mechanically joining a second heat dissipator (12) to the first heat dissipator (9).
The fabrication method that is stipulated as described above is consistent with an assembly method for assembling the previously described heat-dissipating device of the semiconductor device according to the present invention, and the order of this assembly need not correspond to the order in the description.
A step of forming a depression 3 in the second wiring substrate (2) in a direction that is orthogonal to the second substrate surface (5) of the second wiring substrate (2) is further added. The third joining step involves insetting the first wiring substrate (1) into this depression (3) to make the planar direction, in which conductors (6) extend, parallel to the first substrate active surface (4) of the first wiring substrate (1) and the second substrate surface (5) of the second wiring substrate (2). The second joining step involves joining the first heat dissipator (9) to the first wiring substrate (1) with a heat conductive adhesive layer (8) interposed. The fifth joining step involves joining the second heat dissipator (12) to the first heat dissipator (9) with a heat conductive buffer layer (11) interposed. As previously explained, a sixth joining step for joining a third heat dissipator (17) to the second wiring substrate (2) is also important. The sixth joining step involves joining the third heat dissipator (17) to the second wiring substrate (2) with a heat conductive buffer layer (16) interposed.
The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings, which illustrate examples of preferred embodiments of the present invention.